Can a CT (Computed Tomography) calcium score diagnose atherosclerotic cardiovascular disease?

CT Calcium Score for Diagnosing Atherosclerotic Cardiovascular Disease

CT calcium scoring is a reliable marker of coronary atherosclerosis but is not a diagnostic test for obstructive coronary artery disease due to its modest relationship with coronary stenosis. 1, 2

What CT Calcium Scoring Measures

• CT calcium scoring quantifies coronary artery calcification, which serves as a marker of atherosclerotic burden and vascular age 2
• Coronary calcifications are exclusively present in atherosclerotic lesions of the intimal layer, representing the presence of atherosclerosis 3
• The scan is performed using ECG-gated multidetector computed tomography with relatively low radiation exposure (0.37-1.5 mSv) 2

Diagnostic Value for Atherosclerosis

• Calcium scoring definitively establishes the presence of atherosclerosis, as calcification does not occur in normal vessel walls 1
• The degree of coronary calcification correlates with the extent of total atherosclerotic burden, with cardiovascular risk increasing proportionally to the calcium score 3
• The Agatston score is the most widely used scoring system, defining calcific lesions as having CT density >130 Hounsfield units and area >1 mm² 4

Limitations as a Diagnostic Tool

• CT calcium scoring has poor specificity for diagnosing obstructive coronary artery disease due to the modest relationship between calcification and luminal obstruction 1
• In symptomatic patients with zero calcium score, studies have shown that 3.5% still had ≥50% arterial stenosis and 1.4% had ≥70% stenosis 4
• Calcium scoring cannot detect non-calcified atherosclerotic plaques, which may be present in earlier stages of atherosclerosis 4
• CT calcium scoring should be seen primarily as a marker of atherosclerosis and not of degree of stenosis 2

Clinical Applications

• CT calcium scoring is most valuable for risk stratification in asymptomatic individuals with intermediate (7.5-20%) or borderline (5-7.5%) 10-year ASCVD risk 1, 2
• A calcium score of zero indicates excellent prognosis with very low risk (<1% annually) for cardiac death or myocardial infarction 2, 4
• High calcium scores (≥400) indicate severe plaque burden and are associated with increased risk of major adverse cardiovascular events 5
• Intermediate-risk patients without coronary artery calcification can be reclassified into a lower-risk group, potentially avoiding statin therapy 1, 2

When to Use CT Calcium Scoring

• Most appropriate for asymptomatic individuals aged 40-75 years with intermediate ASCVD risk to guide preventive therapy decisions 2
• Not recommended for men under 40 and women under 50 years due to low prevalence of calcification in younger individuals 2
• Not recommended as a surrogate for angiographic disease detection in symptomatic patients 1
• Should not be used for repeated testing too frequently, as changes in calcium scores occur slowly over time 6

Alternative Diagnostic Approaches for Obstructive CAD

• For diagnosing obstructive coronary artery disease in symptomatic patients, other modalities are more appropriate:
  • CT coronary angiography provides direct visualization of coronary stenosis 7
  • Stress myocardial perfusion imaging offers high diagnostic accuracy in symptomatic women with intermediate to high risk of CAD 1
  • Functional testing may be needed if CT angiography shows uncertain functional significance of stenosis 3

In conclusion, while CT calcium scoring is an excellent tool for detecting the presence of atherosclerosis and stratifying cardiovascular risk, it should not be relied upon as a standalone diagnostic test for obstructive coronary artery disease due to its limited specificity for stenosis.